It is planned to carry out an extensive investigation of two areas of statistical methodology which have direct relevance to the analysis of data arising from experimental studies, planned or observational, in environmental health and epidemiology. The ultimate objective would be to provide more efficient statistical methodology to achieve valid conclusions at less cost in terms of time and sample size. The frst area concerns the analysis of incomplete response-time (e.g., survival) data obtained from etiologic research studies to evaluate the effect of various risk factors in relation to a given disease. Included will be such topics as the efficient design of the experimental study, estimation of the entire response time distribution, regression analysis in which levels of environmental, prognostic and other risk factors are entered as covariate values. Both parametric and nonparametric approaches will be utilized. The second area is that of adaptive sequential sampling in medical trials with several competing treatments. The properties of various rules (adaptive, eliminating, randomized, etc.) will be investigated and compared with respect to several criteria, such as expected total sample size required (or mean duration of the study), and expected number of observations from inferior treatments.